Fixed clicking global Duo Chat button after dismissed callout

Changelog: fixed
EE: true

ee/app/assets/javascripts/ai/components/global_callout/duo_chat_callout.vue

@@ -43,7 +43,9 @@ export default {
   },
   methods: {
     handleButtonClick() {
-      this.$refs.popoverLink.$emit('click');
+      if (this.$refs.popoverLink) {
+        this.$refs.popoverLink.$emit('click');
+      }
     },
     stopListeningToPopover() {
       if (this.popoverTarget) {

ee/spec/frontend/ai/components/global_callout/duo_chat_callout_spec.js

@@ -146,5 +146,10 @@ describe('DuoChatCallout', () => {
       findFirstTargetElement().click();
       expect(userCalloutDismissSpy).toHaveBeenCalledTimes(1);
     });
+
+    it('does not fail if the chat button is clicked after callout was dismissed', () => {
+      createComponent({ shouldShowCallout: false });
+      expect(() => findFirstTargetElement().click()).not.toThrow();
+    });
   });
 });